The present invention relates to a refrigerant cycle apparatus which comprises a compressor, a gas cooler, throttling means, and an evaporator, which are sequentially connected to form a refrigerant circuit.
In a conventional refrigerant cycle apparatuses of this kind, a rotary compressor (compressor), a gas cooler, throttling means (capillary tube, etc.), and an evaporator, etc., are formed into a sequential loop through piping connection to make up a refrigerant cycle (refrigerant circuit). Refrigerant gas is taken into the low pressure chamber side of a cylinder by entering from a suction port of a rotary compression element in a rotary compressor, and it is compressed into high-pressure, high-temperature refrigerant gas through the workings of rollers and vanes, and the compressed gas is discharged from the high pressure chamber side into a gas cooler by going through a discharge port and a discharge silencing chamber. After heat dissipation at the gas cooler, the refrigerant gas is throttled by throttling means to be fed to an evaporator. As the refrigerant evaporates there, it absorbs heat from the surroundings at that time, thereby exerting a cooling effect of the conventional art (e.g., refer to Japanese Patent Publication No. 7-18602 Gazette).
However, in a case where such a refrigerant cycle apparatus adopts a type of a compressor whose pressure inside its sealed vessel tends to become high (internal high pressure), because refrigerant gas having a high temperature and a high pressure is discharged in the sealed vessel, the temperature of the compressor itself goes up, which then raises the temperature of refrigerant to be taken into a compression element of the compressor, causing a conventional problem of an reduced compression efficiency.
To deal with that problem, there has been a conventional contrivance of a refrigerant cycle apparatus which employs a multi-stage compression type compressor to perform an intermediate cooling of refrigerant under compression. That is, in addition to employing a multi-stage compression type compressor having the first and the second compression elements, such an apparatus adopts a configuration having an intermediate cooling circuit, which allows refrigerant compressed in the first compression element (the first tier) to dissipate heat, where, after heat dissipation of the refrigerant compressed in the first compression element at the intermediate cooling circuit, it is taken in the second compression element (the second tier) to be compressed there, and the compression is discharged in the sealed vessel. With such a configuration, it is possible to cool the refrigerant compressed in the first compression element, improving compression efficiency at the second compression element. In addition, the cooling of the refrigerant gas to be taken into the second compression element makes it possible to reduce the temperature rise of the refrigerant gas to be compressed in the second compression element and to be discharged in the sealed vessel, gas cooler, etc, which makes it further possible to enhance the cooling capability at the evaporator.
However, in a case where an intermediate cooling circuit is employed to cool down refrigerant compressed in the first compression element as described above, as illustrated in FIG. 4, a part of the refrigerant may be liquefied due to effects from outside-air temperature or depending on the operating conditions of a compressor, etc. Namely, there has been a conventional problem in that refrigerant may be put into a two-phase mixed state of gas/liquid (state (3) in FIG. 4), and if taken into the second compression element without any countermeasures taken, liquid compression would occur at the second compression element, suffering damage.